This invention is generally relative to a multiuser direct sequence spread spectrum (DSSS) Orthogonal Frequency Division Multiplexing (OFDM) multiband based Ultra Wideband (UWB) Communications for short-distance wireless broadband communications.
U.S. Federal Communications Commission (FCC) released a revision of Part 15 of Commission's rules regarding UWB transmission systems to allow marketing and operation of certain types of new products incorporating UWB technology on Apr. 22, 2002. Using spectrums occupied by existing radio service, an UWB device can operate without causing interference, thereby permitting scarce spectrum resources to be used more efficiently. Thus, it is feasible that the UWB technology is able to provide significant benefits for Government, public safety, businesses and consumers within an operation spectrum.
In general, FCC is adapting unwanted emission limits for UWB communication devices that are significantly more stringent than those imposed on other Part 15 devices. In indoor environments of UWB operations, FCC allows a wide variety of the UWB communication devices, such as high-speed home and business networking devices, subject to certain frequency and power limitations. An emission limitation is −10 dBm for indoor UWB operations. The UWB communication devices must operate in the frequency band from 3.1 GHz to 10.6 GHz. In addition, the UWB communication devices should satisfy the Part 15.209 emission mask limitations for the frequency band below 960 MHz and above 960 MHz.
For the UWB communication devices operating in indoor environments, Table 1 lists FCC restrictions of the emission masks (dBm) along with the frequency bands (GHz) as follows:
TABLE 1Frequency (MHz)EIRP (dBm) 0-960−41.3 960-1610−75.31610-1990−53.31990-3100−51.3 3100-10600−41.3Above 10600−51.3
FCC defines an UWB communication device where a fractional bandwidth is greater than 0.25 given by,
                              FB          =                      2            ⁢                          (                                                                    f                    H                                    -                                      f                    L                                                                                        f                    H                                    +                                      f                    L                                                              )                                      ,                            (        1        )            where fH is the upper frequency of −10 dBm emission point, and fL is the lower frequency of −10 dBm emission point. The center frequency Fc of an UWB transmission system is obtained by using average of the upper and lower −10 dBm points as follows:
                              F          C                =                                                            f                H                            +                              f                L                                      2                    .                                    (        2        )            Furthermore, a minimum frequency bandwidth of 500 MHz must be used for any indoor UWB communication devices regardless of the center frequency.
As can be seen, the UWB communication devices must be designed in such a way that the indoor UWB operations can only occur in the indoor environments according to indoor UWB emission masks given in Table 1. The UWB communication devices can be used for wireless broadband communications, particularly for a short-range high-speed data transmission that can be considered as broadband access to networks.
Given an frequency band from 3.1 GHz to 10.6 GHz as a single frequency band, an analog-to-digital (A/D) converter and a digital-to-analog (D/A) converter must operate at a very high sampling rate Fs so that an UWB communication receiver can be implemented in a digital domain. This leads to a high requirement for the A/D and D/A converters for UWB transmitter and receiver. Presently, developing such very high-speed A/D and D/A converters may not be possible with a reasonable cost. Thereby, it is a difficult problem to apply the A/D and the D/A converters directly for an UWB communication transceiver based on a single frequency band solution. On the other hand, a single frequency band-based UWB communication transceiver does not have a flexibility and scalability for transmitting and receiving a user data. In addition, the single frequency band-based UWB communication transceiver may have an interference with a wireless local area network (WLAN) 802.11a transceiver without using a special filter system or other approaches since the WLAN 802.11a transceiver operates at a lower U-NII frequency range from 5.15 GHz to 5.35 GHz and at an upper U-NII upper frequency range from 5.725 GHz to 5.825 GHz.
An OFDM is an orthogonal multicarrier modulation technique that has been extensively used in a digital audio and video broadcasting, and the WLAN 802.11a. The OFDM has its capability of multifold increasing symbol duration. With increasing the number of subcarriers, the frequency selectivity of a channel may be reduced so that each subcarrier experiences flat fading. Thus, an OFDM approach has been shown in a particular useful for wireless broadband communications over fading channels.
A DSSS approach is to use a pseudorandom (PN) sequence to spread a user signal. The PN sequence is a stream of binary ones and zeros referred to as chips rather than bits. The DSSS approach can be used to separate signals coming from multiusers. Multiple access interference (MAI) among multiusers can be avoided if a set of PN sequences is designed in such a way that a low crosscorrelation among the PN sequences is obtained.
The multiuser DSSS-OFDM multiband for UWB communications is disclosed herein according to some embodiments of the present invention. The present invention uses eleven frequency bands as a multiband, each of the frequency bands having 650 MHz bandwidths along with OFDM modulation for a multiuser UWB communication transceiver. A multiband OFDM solution allows using a low speed of the A/D and D/A converters. Moreover, a unique of the PN sequences is assigned to each user so that the multiusers can share the same each of the frequency bands to transmit and receive data based on OFDM multiband of UWB technologies. On the other hand, since the OFDM is an orthogonal multicarrier modulation, subcarriers within each of the frequency bands may be flexibility turned on or off. This can lead to avoid the interference with the WLAN 802.11a transceiver during the indoor UWB operations. In addition, the present invention of the multiuser DSSS-OFDM multiband for UWB communications has a scalability to transmit and receive from a data rate of 503.732 Mbps by using only one of the frequency bands to the data rate of 5.541 Gbps by using all of the eleven frequency bands (or a multiband).
Thus, there is a continuing need of the multiuser DSSS-OFDM multiband for an UWB communication transceiver employing an new architecture of the PN sequences, OFDM multicarrier multiband, and filtering for the indoor UWB operations.